LIMOPSIS. 159 



cial beds, but its habitation is now restricted to higher 

 latitudes. Both of these species belong to the genus 

 Leda. 



Genus III. LIMOFSIS *, Sassi. PL IV. f. 8. 



BODY longitudinally oval, or inclining to a circular shape : 

 mantle open on all sides except the back : foot long, slender, 

 and pointed at each end. 



SHELL shaped like the body, nearly equal-sided, porcel- 

 lanous : epidermis hairy or fibrous : beaks incurved and diverg- 

 ing from each other in the course of growth : cartilage thick, 

 contained in a shallow triangular cavity or depression, which 

 is placed directly under the beaks and outside the hinge-plate : 

 teeth tubercular, arranged in a continuous and curved line : 

 pallial scar entire. 



This remarkable, and what some would call " critical/' 

 genus is related intrinsically to Leda, and extrinsically 

 to Pectunculus. Like the former, it has a cartilage, 

 with a cavity for its reception ; but this process is not 

 placed, as in Leda, inside the shell, but on the hinge- 

 line and between the beaks and the hinge-plate. Pec- 

 tunculus has no cartilage ; and its shell is kept closed 

 behind by a ligament, which is wanting in Limopsis. 

 The teeth are arranged in a single continuous row, as in 

 Pectunculus, instead of in two separate rows in the same 

 line, as in Leda. The shape of the teeth in the present 

 genus is intermediate between that of Leda and Pectun- 

 culus, being erect but blunt. The contour of the shell 

 is much more like that of the last-mentioned genus, but 

 it is somewhat longer in proportion to its breadth. 

 Limopsis has scarcely any resemblance to Lima. Al- 

 though the back of the shell in both these genera is fur- 

 nished with a small wing or prolongation on the upper 

 part of each side, and the cartilage-pit is similar, Lima 



* From ite supposed resemblance to the genus Lima. 



